The invention relates to a support for supporting a substrate during plasma processing in a chamber.
Integrated circuits are fabricated by placing a substrate on a support in a chamber, introducing gas into the chamber, and energizing the gas by coupling RF energy to the gas to form a plasma. The support typically comprises dielectric covering an electrode. The gas in the chamber is energized by applying an RF voltage to the electrode and electrically grounding a facing conductor surface in the chamber. The support comprises one or more conduits that extend through the dielectric and electrode, such as gas conduits for supplying heat transfer gas to the interface between the substrate and the dielectric, and other conduits to hold lift-pins that raise or lower the substrate onto the support. It is desirable to extend the edge or extremity of the electrode in the support as close as possible to the conduits to allow a relatively uniform level of RF energy to be coupled to the overlying plasma--even across the electrode gap created by the conduits. However, the proximity of the edge of the electrode to the conduit can result in electrical coupling of the RF energy from the electrode edge to the gas in the conduit. This RF coupling leads to ionization, arcing, and glow discharge of the gas in the conduit. This is undesirable because it causes sputtering, chemical erosion and thermal degradation of the conduit surfaces, the support, and even the backside of the overlying substrate.
Plasma formation in conduits is especially a problem for ceramic dielectric supports. Ceramic supports made from alumina are being increasingly used due to their resistance to chemical erosion and their ability to withstand high temperatures. However, such ceramic supports typically have large diameter conduits because it is difficult to machine small diameter conduits in the brittle ceramic material. A conduit having a large diameter provides a longer pathway in the gap of the conduit for the acceleration of ionized gas molecules. The longer pathway results in a larger number of energetic collisions between charged gas species and other gas molecules which results in avalanche breakdown and plasma formation in the conduit.
Thus there is a need for a support that reduces the incidence of arcing, glow discharge, or plasma formation in conduits that extend through the support during processing of a substrate in the chamber. There is also a need for a support that exhibits reduced erosion and thermal degradation in the chamber. It is further desirable to have a support that provides a more uniform plasma sheath across the surface of the substrate.